|GM Supplemental Vacuum Pump for EVs|
Twenty or 30 years ago, the components for EV conversions were quite a bit less sophisticated,
but one problem seldom cropped up -- providing vacuum for the power brakes. Most small cars,
the vehicles usually converted, were light and had no need for power brakes.|
Few ICEVs today have manual brakes, though. The power brake systems fitted to even the smallest cars these days depend on engine vacuum to supplement your own foot pressure on the brake pedal. The brake systems assume some boost will be present. In most cases the result is brakes which are either uncomfortable to apply, or (in some cases) can barely stop the car, even when you stomp the pedal with all your might!
So when you convert the car, you have to provide some source of vacuum for the power brakes.
A couple of off-the-shelf (or almost) solutions exist.
The traditional answer, used in conversions for decades, is a Gast or other commercial 12 volt vacuum pump. It's not really an EV part, but it's often been drafted for the purpose. It'll require an external reservoir, vacuum switch, and usually a relay. Most of the EV parts suppliers offer pumps and complete kits. The cost is around $350-400 for a kit, around $275-300 for a bare pump.
For a more modern approach, try the MES-DEA vacuum pump. This Swiss-made unit is significantly smaller, lighter, and quieter than the Gast pumps. It's a one-piece, bolt-in system specifically designed for conversion EVs. The vacuum switch is built in. It doesn't have a vacuum reservoir, but a quick and dirty answer is to fix several feet of vacuum hose on the hose barb and wind it round the pump. This pump has been offered in past years by Brusa and Solectria and is currently available through Metric Mind. They offer two models with different capacities. At this writing the smaller and cheaper one costs $285 and the more powerful model is $375. The dollar price varies with the Euro : Dollar exchange rate so check the website for the current price.
If $300-400 seems like a lot to pay, you might try to find a used GM vacuum pump. These were fitted to several models of 1980s-vintage GM cars whose engines didn't produce enough vacuum to make the power brake servo happy.
Most folks will probably want to try to find a boneyard pump. Especially since these are going to be in the range of 20 years old and hard to find, it's a good idea to test the pump at the yard to be sure it runs and pumps. Then check it once you get home to make sure it holds vacuum and operates at the correct pressure.
You can find these pumps on the following cars at the auto recyclers':
In boneyard cars, you'll find the pump on the driver's side front fender well. There's a small (carbon) filter that is on the line just before the pump. Insist on getting the filter with it. You also want the electrical plug that goes to the pump and the rubber mounting plate. You may have to go out in the yard with the torch jockey to show him what you're talking about.
From left to right on the lugs, the first lug is 12 volt power, UNswitched. The second one from the left is
ignition switch or toggle switch; this is a low current trigger which starts the pump. The fourth one is ground.
Can't find a used one? That's no surprise, given the age of the pumps and the cars they were used in. The pump was at one time available new from GM, as part number 22034995. It seems to be a discontinued item now, but you may be able to find old dealer stock.
The problem is the parts counter price -- $300, if you can even find it. This doesn't seem like much of a bargain when Metric Mind's lower cost MES-DEA pump, specifically designed for EVs, is actually a little cheaper.